How are solar panels made? It starts with a grain of sand…
- 27 Jun 2023
- 6 min
Take a cauldron, add three measures of fluxweed, two bundles of knotgrass, and stir four times, clockwise. Just kidding! The process of turning sand into a panel is complicated but there is no magic behind it. In this article, we’ll learn about how solar panels are made.
Key stages of solar panel manufacturing
Silicon is the main component of 95% of solar panels. It is the eighth most common element in the universe and the second most common element in the Earth’s crust. It rarely occurs in its pure form.
The most common compound of silicon, silicon dioxide, or SiO2, can be found in sand and many rocks. It’s not good enough for making solar panels and must be turned into high-purity silicon.
Let’s say, you’ve got your hands on some silicon dioxide. Here is how you make a solar panel out of it.
Step 1: From sand to silicon
First, take silicon gravel and some carbon from coal, coke, or wood chips. Heat them in an electric arc furnace at 3600 °F to start the reduction process and remove oxygen from silicon dioxide. As a result, you’ll get 99% — two nines, or 2N — pure metallurgical-grade silicon.
Still not good enough for panels! You must turn it into even more pure solar-grade polysilicon. During this upgrading, 2N silicon reacts with hydrochloric acid and hydrogen gas and becomes 8N–11N pure solar-grade polysilicon.
Step 2: From silicon to ingots
Melt the silicon again at about 2600°F and dope it with boron to give it a positive charge. Then you need to choose whether the ingot will become a monocrystalline panel or a polycrystalline panel.
To make a polycrystalline ingot, you pour the molten silicon into a rectangular crucible. It cools down, resolidifies and you get a square-shaped ingot.
A monocrystalline ingot is formed by dipping a rod-mounted seed crystal into the melt and slowly pulling it upwards, growing a large cylinder of a single crystal. It’s called the Czochralski method and looks a little like making cotton candy.
The differences in the manufacturing process impact the efficiency of future solar panels. Polycrystalline PV modules convert 15-20% of sunlight into electricity. Monocrystalline panels are harder to make but their efficiency ranges from 18% to 23%. They are 20–25% more expensive than polypanels.
Step 3: From ingots to wafers
Back to ingots. Chop them into smaller bricks, grind, polish, and glue them to a glass plate. After that, slowly move them through a mesh of diamond-coated wires, and they fall into many paper-thin wafers. Put them into a chemical bath to dissolve the glue.
About one-third of the ingot is wasted as sawdust at this step
Step 4: From wafers to cells
First, etch the wafers to remove surface damage, then texturize to reduce reflection losses, and clean to prepare for diffusion. Load the wafers into a diffusion furnace. During heating, phosphorus penetrates the heated positive-type silicon wafers, giving them a negative surface. Thus the positive-negative (p-n) junction forms, where electricity happens.
One cell contains 111 mg of silver which accounts for about 10% of its cost
Clean them again and cover with an anti-reflection coating to increase the amount of light absorbed. Finally, print silver contact patterns on the front side and aluminum contact patterns on the rear side. These patterns will transport the current.
Step 5: From cells to a panel
Solar cells are fragile and have small power output. To make them a real power source, connect them into strings, negative contact to positive contact, and form an array. Encapsulate this array with ethylene vinyl acetate (EVA) and cover it with thin glass from the sun-facing side and backsheet from the back side. Finally, add a junction box and a frame to complete the module. Now the solar cells are sealed and all-weather-ready. Congratulations! You’ve made a solar panel.
Certifications and standards
Before entering the market, a panel needs to demonstrate that it is safe and performs as promised in terms of efficiency, reliability, sustainability, and many other criteria. Conformity is assessed based on standards. You might have seen some while reviewing solar panel specifications.
IEC: International Electrotechnical Commission
The IEC is the world’s leading organization establishing international standards for all electrical, electronic, and related technologies, including solar panels. These standards serve as the basis for testing, inspection, and certification.
Living on the coast? Check your solar panels for IEC 61701 salt mist corrosion and humidity resistance. It’s a must if you live in exceptionally rainy coastal Alaska, for example. For the blistering heat of Phoenix, there is a different certificate — IEC 61215.
UL: Underwriters Laboratories
The UL is a global safety science company based in the United States. It is composed of three organizations: UL Research Institutes, UL Standards & Engagement, and UL Solutions. This facility translates scientific discoveries into standards and policies.
Conformity with the standards of these two major organizations serves as proof that a solar panel is safe to use and performs according to expectations.
Sustainability issues of solar industry
As the solar industry grows, so do concerns about its environmental impact. Making solar panels not only requires caustic chemicals, water, and electricity but also produces greenhouse gases and hazardous waste. Coal generates over 60% of the electricity used for global solar panel manufacturing, according to the IEA’s report.
Luckily, solar panels only need to operate for 4–8 months to offset their production emissions. With a minimum lifespan of 25–30 years, they more than make up for the damage they do.
Another problem is that we don’t have a good way to dispose of old modules yet. Aluminum and glass from solar panels are hard to reuse. The US plans to launch a recycling center in Washington by 2025. There are also private companies that are ready to take on this problem, such as Solarcycle.
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